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Power supplies for sensitive analog front-end electronics is a delicate point that requires significant attention in large scale systems. Power supplies must be used in a fashion compatible to the defined grounding scheme (the configuration of power supplies is strongly linked to general grounding). Analog front-end electronics is in many cases extremely sensitive to noise in the power supply because of the single ended nature of detector signals.

The question of location of the power supply units and the related transfer of power on cables often have significant problems. Low frequency voltage drops on cables can to a large degree be compensated for by the use of remote sensing to compensate for cable losses. Remote sense can on the other hand also pose stability problems as the compensation loop must be stable under large load variations and with different cable characteristics. In special cases the remote sense circuit must be specially adapted to the final working conditions. High frequency components can only be handled with the use of local decoupling capacitors.

In most cases a difficult choice must be made between using normal commercial power supplies in the counting room with long cables (~80m) to the front-end electronics in the detector, or having power supplies in the cavern close to the experiment but then having to deal with radiation and magnetic fields. Power supplies for the use in the cavern must be specially designed to handle the radiation effects and the magnetic fields. For the general LHC experiments only few companies are being considered to be capable of supplying power supplies that can handle the environments of the experimental caverns. The Silicon Tracker colaboration has decided to use the MARATON power supplies from Wiener which will located in the cavern.

A special set of radiation tolerant linear regulators have been developed for the LHC experiments. The Silicon Tracker uses intensively the L4913 regulators for power regulation and distribution in the Service Boxes.

For the sensors bias voltage (we call it high voltage although it can not be considered as such since it goes only up to 500V), a standard (non radiation resistant) solution from CAEN has been adopted. These systems are widely used in high energy physics and have proven to be very reliable.

Hardware and software for the integration of the HV and LV in the LHCb ECS system will be available.

A set of general points to be aware of in the design of the power distribution and grounding and shielding scheme are:

  • Prevent ground loops via power supplies when ever possible.

  • Use floating low voltage power supplies.

  • Use twisted power cables to minimize noise pickup/generation.

  • Use remote sense to compensate for voltage drops on cables.

  • Remote sense must be fully differential to minimize noise pick up.

  • Remote sense must be capable of compensation for voltage drop in power supply return (known problem with radiation tolerant linear regulators from ST).

  • Take special care of high voltage and its distribution.

  • No single point failure must generate safety hazards (e.g. high voltage connected to accessible structure).

  • Separate if possible power supplies for analog front-end from power supplies for digital logic.

  • Sudden power consumption drop may generate serious over-voltage on load. Extensive local decoupling and over voltage protection may be needed.

  • Magnetic coils/transformers and cooling fans in power supplies are sensitive to magnetic fields.

  • Power supplies are known to be sensitive to single event burn-out caused by hadrons.

  • Switching mode power supplies are known to in some cases to generate significant common mode noise.

  • ...

The following figure shows and simplified alltoghether scheme with the LV power supply lines, HV and grounding for the Silicon Tracker. The scheme is more intended for the the Inner Tracker detector, but it can be easily extended for the Trigger Tracker.

Silicon Tracker grounding scheme